Natural nodulation of Acacia mangium–Acacia auriculiformis hybrids: distribution of the indigenous strains in the nodules

Polymerase Chain Reaction/Restriction Fragment Length Polymorphism (PCR/RFLP) of the InterGenic Spacer (IGS) between rDNA 16S and 23S was used to identify indigenous strains nodulating four clones of Acacia mangium–Acacia auriculiformis hybrids cultivated in non-sterilized sandy soil from Sangalkam (Senegal) under greenhouse conditions. The experiment was for 4 months. The analysis of restriction fragment length polymorphism obtained with MspI and HaeIII restriction enzymes allowed the identification of 15 different IGS Groups with a distribution which significantly differed according to the clone of the hybrid (strains of one clone can belong to three and five different IGS Groups). Three large multi-lobed nodules were obtained on the root system of clone 3.26 within 5 months. Also, the nature of the rhizobia contained in each lobe was determined. The results showed that the lobes of large nodules can be occupied by one or two strains and the nodules analysed were mainly occupied by those belonging to IGS Group 12.